Effect of Fertilizer Application on the Yield of Walnut (Juglans regia L.)

Anmin MIN Fanrong ZHENG Li ZHANG Jianshe HE Changxu YANG Qianli LIU Li WANG,Yu WANG Hongxia LI

Abstract [Objectives]This study was conducted to explore the fertilization ratio of walnut， so as to provide a basis for rational fertilization of walnut.[Methods]Under the condition of gravelly yellow soil in Chaotian District， Guangyuan City， the orthogonal design of L9 （34） was used to test the fertilization ratio of nitrogen， phosphorus and potassium fertilizers.[Results]The effects of nitrogen， phosphorus and potassium fertilizers on walnut yield ranked as phosphate fertilizer>potassium fertilizer>nitrogen fertilizer. The different treatments had great effects on the yield of walnut， and for the land with gravelly yellow soil， the suitable annual fertilization amount of walnut was urea 1 200 g/plant + calcium superphosphate 1 500 g/plant + potassium sulfate 940 g/plant.[Conclusions]This study provides a theoretical basis for rational fertilization of walnut in Sichuan Province.

Key words Juglans regia L.; Nitrogen; Phosphorus; Potassium; Fertilizer; Yield

Walnut （Juglans regia L.） is a deciduous tree in Juglans of Juglanaceae， also known as Qiangtao， native to the Near East. Walnut is an important nut and woody oil tree with high nutritional and economic value， ranking first among the four major dried fruits[1]. Walnut has a long history of cultivation in Sichuan， and its natural distribution is extremely extensive， covering almost all parts of the province except the plateau in Northwest Sichuan. It is a common dry fruit and woody oil tree species cultivated in Sichuan Province， and the annual output of walnut is among the best in China[1]. In the past two decades， many areas in the province have set off a boom in walnut planting combining with the construction of "returning farmland to forests" and the adjustment of agricultural structure， and walnut planting has become a pillar industry for farmers in some mountainous areas to increase their incomes. With the rapid expansion of the development of walnut in the province， the problems in cultivation and management have become increasingly prominent. Among them， fertilization management has become one of the key links that restrict the increase of walnut yield and benefit[2]. Domestic researches on walnuts mostly focus on germplasm resources[3-6]， breeding[7-11]， seedling breeding[12-15]， grafting[16-20]， pruning[21-24]， organ tissue nutrients and their variation[25-28]and pest control[29]. In the field of walnut fertilization， there are related literatures in China[30-32]. Due to the change of soil fertility status， it will inevitably lead to the difference in fertilization ratio of walnut. Directing at the soil conditions in Sichuan， few reports have been conducted on the fertilization of walnut. In order to adapt to the demand for fertilization management of walnut in production in Sichuan Province， an experiment of the combined application of nitrogen， phosphorus and potassium fertilizers to the walnut fruit trees was carried out to explore the fertilization ratio of walnuts， so as to provide a basis for rational fertilization of walnuts in Sichuan Province.

Materials and Methods

General situation of the experimental field

The test site is located in Nanhua Village， Shahe Town， Chaotian District， Guangyuan City， with an altitude of 527 m. This area has a low mountain terrain with a slope of 15°-25°. The soil is the gravelly yellow soil developed from sandstone and slide rock， with a thickness of the soil layer of 30-60 cm. The soil is neutral to slightly alkaline， and contains slightly lower soil organic matter， total nitrogen， total phosphorus and available potassium， and moderate total potassium， hydrolyzed nitrogen and available phosphorus content. The soil belongs to clay， which is slightly heavier with better physical properties and has better water retention and fertilizer retention capacity （Table 1， Table 2）. The test area has a subtropical humid monsoon climate， with a mean annual precipitation of 980 mm， mostly concentrated in May to October. The climate is humid with sufficient rainfall and suitable light， and the four seasons are distinct. Because this area is located at the central part of the Qinba Mountain area where the cold and warm air convection currents meet， it is rainy in summer and autumn and windy in winter and spring; the annual average temperature is 12-15， the annual extreme high temperature is 38-39， and the extreme low temperature is -9.1--8.2; and the frostfree period is 192 to 250 d. The water system is the Jialing River basin.

The experiment was carried out in a walnut plantation with relatively uniform site conditions where the trees grew relatively uniform at an afforestation density of 625 plants/hm2 （plant spacing 4 m≠4 m）. The afforestation time in the experimental site was in spring of 2004.

Experimental materials

The fertilization objects were walnut trees of 12 years old. The trees were subjected to variety improvement at the third year of afforestation by bud grafting method. The grafted walnut variety was the excellent variety "Suoxing" which was locally selected.

Test fertilizers： Urea（NH2）2CO （N： 46%）; calcium superphosphateCa （H2PO4）2·H2O （P2O5： 12%）; potassium sulfateK2SO4 （K2O： 50%）.

Experiment design

（1） Fertilization factors and levels： The applied fertilizers and their application rates are shown in Table 3.

（2） Test treatment： The experiment adopted the L9 （34） orthogonal design[33]with the three factors and three levels， forming nine treatments. With no fertilizer as the check （CK） treatment， a total of 10 treatments were as follows： 1 N1P1K1， 2 N1P2K2， 3 N1P3K3， 4 N2P1K3， 5 N2P2K1， 6 N2P3K2， 7 N3P1K2， 8 N3P2K3， 9 N3P3K1， 10 N0P0K0 （CK）.

（3） Experimental field arrangement： The plots were randomly arranged[33]. Each treatment plot included five plants， with 4 replicates. The experiment field had an area of 1 hm2.

Methods

（1） Fertilization time and method： According to the annual growth characteristics of walnut， the fertilization was performed twice. The first time of fertilization was carried out before the spring germination with an application amount 60% of the total amount， and the second time was performed in the young fruit development period with an application amount accounting for 40% of the total amount in the year. For the sloping land， a semiannular groove was excavated along the projection of the canopy above the slope， and an annular groove was excavated along the projection of the canopy on the flat ground. The fertilizers were uniformly applied to the groove according to the type and amount required by the test treatment and covered with soil.

（2） Yield observation： During harvesting of the mature walnut fruit， the yield was determined by plant.

（3） Data analysis： The test results were statistically analyzed using analysis of variance[33]and range analysis[34].

Results and Analysis

Effect of fertilization on yield of walnut

The statistical results and variance analysis of walnut yield in the experimental field are shown in Table 4 and Table 5， respectively.

According to the results of the twoway analysis of variance （Table 5）， the results of the F test showed that the differences between the treatments were extremely significant. To further analyze the differences between the treatments and the CK， multiple comparisons were performed using L.S.D （Table 6）.

It could be seen from Table 6 and Table 7 that all the nine fertilization treatments had an effect of increasing walnut yield compared with the CK， and the yield increases ranked as treatment 4>treatment 7>treatment 8>treatment 6>treatment 3>treatment 5>treatment 1> treatment 9>treatment 2 >treatment 10 （CK）. The combined fertilization treatment 4 was the best， followed by treatment 7， and they increased the yield by 42.36% and 31.24%， respectively. The yield differences between fertilization treatments 4， 7， 8 and 6 were extremely significant. The yields of fertilization test treatments 3， 5 and 1 were significantly different from that of the CK. There were no significant differences between fertilization test treatments 9 and 2 and the CK. Treatment 4 showed an increased yield compared with other nine treatments， and except that there was no significant difference with the yield of treatment 7， the differences with the yields of other eight treatments were extremely significant. Treatment 7 was lower than treatment 4 in yield， but its yield was higher than other eight treatments， with no significant differences from treatments 8 and 6， significant differences from treatments 3 and 5， and extremely significant difference from other four treatments. Treatments 8 and 6 had no significant differences from treatments 3， 5， 1， 9 and 2 in yield， and there were extremely significant differences between the two and the CK. Min et al.[35]studied the nutrient elements in the leaf and fruit of walnut at the fruiting stage， and the results showed that walnut had a higher demand for nitrogen and potassium elements. The results also showed that the combined fertilizer treatment that met this demand exhibited a yield obviously higher than other treatments， achieving an obvious fertilization effect.

Primary and secondary analysis of nitrogen， phosphorus and potassium efficiency

The ranges of walnut yield under different application levels of nitrogen， phosphorus and potassium elements are shown in Table 8. It could be seen that the range of walnut yield under the nitrogen fertilizer of the three fertilization levels was NR=713.3 g/plant， and the yield increase was 11.02%; the phosphate fertilizer showed a range PR=823.9 g/plant， and the yield increase was 12.52%; and the range under the three potassium fertilizer levels was KR=749.1 g/plant， and the yield increased by 11.56%， reflecting that the effects of nitrogen， phosphorus and potassium fertilizers on walnut yield were not the same， which were expressed as phosphate fertilizer>potassium fertilizer>nitrogen fertilizer. Li and Chen et al.[2，36]gave the same result from the study on formula fertilization of walnut. After the walnut enters the fruiting period， it blooms and bears every year， and it needs to absorb and consume a large amount of nutrients in the soil to maintain the trees health and high and stable yield. Therefore， it is equally important to increase the amount of fertilization and increase the application of other nutrient elements[36]to supply its growth with required nutrients in a balanced manner.

Fertilization benefit of fruiting walnut tree

Among the three factors， i.e.， the nitrogen， phosphorus and potassium fertilization levels， the highest fertilizer efficiency was achieved when applying urea at 1 200 g/plant， which achieved an average yield of 7 185.3 g/plant; the application of calcium superphosphate at 1 500 g/plant showed an average yield of 7 404.7 g/plant; and when the potassium sulfate was applied at 940 g/plant， the average yield was 7 228.6 g/plant （Table 8）. It could be seen that the optimized application rates of nitrogen， phosphorus and potassium in walnut were 1200 g/plant of urea， 1 500 g/plant of calcium superphosphate and 940 g/plant of potassium sulfate， which were realized exactly in treatment 4 which achieved the highest walnut yield， namely the mediumlevel nitrogen fertilizer， lowlevel phosphorus fertilizer and highlevel potassium fertilizer in the experimental design， which are closely related to the moderate nitrogen and phosphorus contents and low potassium content in the soil. Chen et al.[36]studied the fertilization of earlyfruiting walnut in Xinjiang， and found that the suitable fertilization amounts of soil with low nitrogen， phosphorus and potassium contents were higher than those of soil with high available nutrient contents， which is consistent with the present study. Therefore， the fertilization ratio of nitrogen， phosphorus and potassium is closely related to soil fertility.

Conclusions

In the matched application of nitrogen， phosphorus and potassium fertilizers， phosphorus fertilizer had the greatest impact on the yield of walnut， followed by potassium fertilizer， and nitrogen fertilizer had the lowest effect.

The different combined treatments of nitrogen， phosphorus and potassium fertilizers had great effects on the yield of walnut. For the land with gravelly yellow soil， the suitable annual fertilization amount of walnut was urea 1 200 g/plant + calcium superphosphate 1 500 g/plant + potassium sulfate 940 g/plant.

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